Various arrangements of electrical leads have been taught previously for enabling integrated circuit packages to be connected to printed circuits, as by soldering individual leads to the printed circuits or by clamping leads between a rigid separate body and contact pads on a printed circuit. The physical space required to permit soldering individual leads or clamping individual leads in place, however, presents certain shortcomings in applications where signals are intended to be transmitted at high frequencies and where there is high signal line density. Also, the length and impedance of individual conductors may be a factor in the circuit design. In such circuits, it becomes desirable, then, to reduce the size of circuits as much as possible, and, for the sake of reducing the cost of production and repair, it is desirable to provide simple and reliable means for connecting components to printed circuits.
The prior art has typically relied upon chip carriers to house electronic components, with such chip carriers being attached to printed circuits either through the use of conductive adhesives (such as reflowed solders or conductive epoxies) or through the use of a third, electrically conductive, and physically and electrically connective socketing part, which resides between the printed circuit and the component housing.
The attachment of electronic component housings to the contact pads of printed circuits using socketing parts is a solderless approach to interconnecting the two units, however, in the prior art a third, physically independent, electrically conductive, mechanically and electrically connective part has generally been required for this type of interconnection.
As an example, gull wing leads of an electronic component housing may be mated to the printed circuit contact pad using a compressible elastomer in a socket such that the rigid pressure bracket of the socket compresses the elastomer down upon the gull wing leads and physically and electrically mates the two contacts. Normally, all of such contacts have a high quality exterior finish with high electrical conductivity, such as by the use of gold, and are considered to have a reliable interconnection when a minimum pressure of approximately 8 to 16 grams is applied to the interface between the contacts. Such pressure has been provided in the past by, for example, corner screws which distribute the force across the socket's rigid pressure bracket such that the pressure at each lead is maintained at the required level.
A rigid insulating socket body, in other devices, retains an array of individual pin leaded spring contact sockets, wherein each contact houses a spring contact which mates, again under pressure, to the component housing pin lead. The socket itself, in such systems, is reflow soldered to the printed circuit contact pad, and conductivity between the component housing body and the printed circuit is again made by way of a component socket.
It is also desirable to provide a compatible electromagnetic environment to act as a suitable vehicle for the conveyance of electronic signals between the printed circuit and the electronic components housed within a component housing, and to supply the signals internally to the electronic components in such a manner as to minimized the total area of circuit board required for the interconnection between the mounted component housing and the printed circuit on which it is mounted.
As the physical size of circuit components is reduced it becomes more and more difficult to make good electrical contact with individual circuit component leads. It is therefore important to provide for reliable electrical connection to the various electrical components located within a housing of reduced size.
Because individual leads previously have had to be connected, by the use of wires or conductive material desposited on flexible films appropriately clamped in place by separate structural members during installation of component housings, the size of conductors and connector pads previously has been larger than would be desired otherwise, in order that desired junctions may be accomplished without inadvertent electrical interconnections of electrical leads which are intended not to be connected to one another. As a result, currently used leads and pads have dimensions which are in many cases much larger than the size needed to carry the anticipated electrical loads.
More recently, devices disclosed in Hutchison U.S. Pat. No. 3,984,166, Modden U.S. Pat. No. 4,458,968, and Hodge et al. U.S. Pat. No. 4,420,767 have disclosed chip carriers capable of solderless connections, but without great advantage in terms of contact density. White et al. U.S. Pat. No. 4,601,526 discloses a chip carrier providing improved contact density.
Along with reduced component size, however, comes added difficulty in making contact for the testing of individual circuit elements.
What is needed, then, is an improved assembly for mounting electronic component housings on printed circuits, making installation simple, accurate, and reliable, and permitting installation of electronic components in a smaller space on a printed circuit than previously was required, while still leaving it possible to test the circuits contained and connected with the electronic components so mounted.